OHIVERSITY  OF  CALIFOBNIA  PUBLICATIONS 

COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


POLLINATION  OF  THE 
BARTLETT  PEAR 


BY 

WARREN   P.  TUFTS 


BULLETIN  No.  307 

May,  1919 


UNIVERSITY  OF  CALIFORNIA  PRESS 

BERKELEY 

1919 


Benjamin  Ide  Wheeler,  President  of  the  University. 

EXPERIMENT  STATION  STAFF 

HEADS    OF   DIVISIONS 

Thomas  Forsyth  Hunt,  Director. 
Edward  J.  Wickson,  Horticulture   (Emeritus). 

Herbert  J.  Webber,  Director  Citrus  Experiment  Station;  Plant  Breeding. 
Hubert  E.  Van  Norman,  Vice-Director;  Dairy  Management. 
William  A.   Setchell,  Botany. 
Myer  E.  Jaffa,  Nutrition. 
Charles  W.  Woodworth,  Entomology. 
Ralph  E.  Smith,  Plant  Pathology. 
J.  Eliot  Coit,  Citrieulture. 
John  W.  Gilmore,  Agronomy. 
Charles  F.  Shaw,  Soil  Technology. 
John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 
Frederic  T.  Bioletti,  Viticulture  and  Enology. 
Warren  T.  Clarke,  Agricultural  Extension. 
John  S.  Burd,  Agricultural  Chemistry. 
Charles  B.  Lipman,  Soil  Chemistry  and  Bacteriology. 
Clarence  M.  Haring,  Veterinary  Science  and  Bacteriology. 
Ernest  B.  Babcock,  Genetics. 
Gordon  H.  True,  Animal  Husbandry. 
James  T.  Barrett,  Plant  Pathology. 
Fritz  W.  Woll,  Animal  Nutrition. 
Walter  Mulford,  Forestry. 
W.  P.  Kelley,  Agricultural  Chemistry. 
H.  J.  Quayle,  Entomology. 
Elwood  Mead,  Rural  Institutions. 
J.  B.  Davidson,  Agricultural  Engineering. 
H.  S.  Reed,  Plant  Physiology. 
D.  T.  Mason,  Forestry. 
C.  L.  Roadhouse,  Dairy  Industry. 
fFRANK  Adams,  Irrigation  Investigations. 
J.  C.  Whitten,  Pomology. 
F.  L.  Griffen,  Agricultural  Education. 
John  E.  Dougherty,  Poultry  Husbandry. 
S.  S.  Rogers,  Olericulture. 
J.  G.  Moodey,  Assistant  to  the  Director. 
Mrs.  D.  L.  Bunnell,  Librarian. 

DIVISION  OF  POMOLOGY 

J.  C.  Whitten  W.  P.  Tufts 

W.  L.  Howard  *E.  L.  Overholser 

R.  H.  Taylor  W.  L.  Sweet 

A.  H.  Hendrickson  G.  L.  Philp 

M.  N.  Wood 


t  In  cooperation  with  Office  of  Public  Roads  and  Rural  Engineering,  U.   S. 
Department  of  Agriculture. 

*  Exchange  Professor  from  Cornell  University,  1918-19. 


POLLINATION   OF  THE   BARTLETT   PEAR 

By  WAEEEN  P.  TUFTS 


There  is  a  growing  interest  on  the  part  of  pear  growers  in  Cali- 
fornia concerning  the  question  of  whether  the  Bartlett,  their  chief 
variety,  requires  or  is  benefited  by  cross-pollination.  The  fact  that 
Bartlett  trees,  planted  without  any  regard  to  cross-pollination,  have 
yielded  profitable  crops  has  led  some  to  believe  that  the  variety  is  self- 
fertile.  On  the  other  hand,  these  same  growers  have  noticed  when 
they  have  a  stray  tree  of  some  other  variety  in  their  orchard  that  the 
surrounding  Bartletts  are  more  abundantly  fruited  than  the  remain- 
der of  the  orchard.  This  seems  to  indicate  that  the  Bartlett,  under 
valley  conditions,  is  greatly  benefited  by  cross-pollination.  In  the 
Sierra  foothills  thoughtful  and  observant  growers  have  felt  sure  that 
the  Bartlett,  under  their  conditions,  is  always  self -sterile,  to  a  degree 
rendering  cross-pollination  imperative. 

Waite1  discovered  several  years  ago  that  the  Kieffer,  a  leading 
variety  of  the  eastern  and  middle  states,  was  practically  self-sterile. 
Since  that  time  there  has  been  much  discussion  throughout  the  country 
as  to  whether  or  not  certain  varieties  besides  the  Kieffer  could  be 
benefited  by  cross-pollination  and  what  varieties  could  be  depended 
upon  to  serve  as  pollinators. 

Fletcher2  states  that : 

The  results  of  hand-pollinating  8408  Kieffer  pear  blossoms  and  9867  Bartlett 
pear  blossoms  in  the  years  1903,  1906,  and  1907  indicate: 

1.  In  West  Virginia  and  Michigan,  and  probably  in  other  parts  of  the  east, 
unsatisfactory  results  may  be  expected  from  planting  either  Bartlett  or  Kieffer  in 
large  blocks  so  that  cross-pollination  by  insects  is  not  general. 

2.  Anjou,  Lawrence,  Duchess,  and  Kieffer  are  satisfactory  varieties  for  plant- 
ing with  Bartlett  so  far  as  pollination  is  concerned.  Some  years  Kieffer  does  not 
blossom  simultaneously  with  Bartlett  but  usually  the  blossoming  seasons  overlap 
sufficiently. 

Kraus3  advises  planting  Clairgeau,  Anjou,  Howell,  or  Kieffer  with 
Bartlett  for  the  purpose  of  effecting  cross-pollination. 

i  Waite,  M.  B.,  Pollination  of  Pear  Flowers,  Bull.  5,  Div.  Veg.  Path.,  U.  S. 
Dept.  Agr.,  1894. 

2  Fletcher,  S.  W.,  Eeport  of  Virginia  Agr.  Exp.  Sta.,  1909-1910. 

s  Kraus,  E.  J.,  The  Pollination  Question,  Ore.  Agr.  Exp.  Sta.,  Cir.  Bull.  No.  20, 
1912. 


370  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Wisker4  says  that: 

California's  pear  profits  would  be  greater  if  some  other  variety  were  planted 
with  Bartlett  for  cross-pollination.  Anjou,  Bose,  and  Cornice  are  good  pollinators 
and  sell  for  higher  prices  than  Bartlett.  We  have  increased  the  fruitfulness  of 
an  old  Bartlett  orchard  more  than  200  per  cent  by  inter -grafting  other  varieties. 

Weldon5  believes  that : 

The  best  results  in  growing  Bartlett  pears  cannot  be  attained  unless  other 
varieties  are  planted  with  them  in  the  orchard.  Despite  the  evidence  that  this 
should  be  done,  there  are  thousands  of  acres  of  Bartletts  being  planted  in 
California  each  season  with  utter  disregard  of  the  benefits  that  might  be  derived 
by  planting  one  or  more  other  varieties  for  cross-pollination.  In  certain  new  pear- 
growiug  sections,  the  writer  has  recently  seen  thousands  of  acres  of  Bartletts 
in  blocks  of  five  acres  to  more  than  one  hundred  acres  each,  with  no  other  varieties 
near,  except  possibly  an  occasional  tree  of  some  favorite  pear  planted  for  home 
use.  In  some  of  these  sections  heavy  winds  and  extremes  of  heat  and  cold  occur, 
making  more  necessary  the  strictest  attention  to  every  detail  that  would  tend  to 
increase  productivity.  The  fruit  in  general  is  good,  and  the  trees  everywhere 
have  done  well.  So  far  as  it  has  been  possible  to  determine,  they  are  self -fertile 
to  a  remarkable  degree  when  the  existing  conditions  are  taken  into  consideration, 
but  it  is  safe  to  predict  that  there  will  be  years  of  short  crops  because  of  the 
absence  of  other  pears,  and  the  average  production  of  these  sections  throughout 
a  series  of  years  will  be  far  below  what  it  would  be  with  other  varieties  planted 
along  with  the  Bartletts  for  cross-pollination  purposes.  There  are  older  pear- 
growing  sections  of  the  state  where  large  areas  of  Bartletts  have  been  planted 
by  themselves  and  where  the  same  arguments  against  the  practice  may  be  used. 

Although  practically  all  writers  agree  in  advising  the  inter-planting 
of  other  varieties  to  pollinate  the  Bartlett,  even  in  the  valley  locations 
in  California,  nevertheless  the  bulk  of  the  acreage  planted  to  Bartletts 
in  the  state  contains  no  other  variety.  The  writer  outlined  and  per- 
formed certain  experiments  during  the  seasons  of  1916,  1917,  and  1918 
designed  to  test  the  accuracy  of  the  observations  enumerated  above. 


THE   PROBLEMS   OF   BARTLETT   PEAR   POLLINATION 

In  planning  the  work  of  which  this  bulletin  is  a  report,  the  writer 
had  in  mind  the  differences  of  altitude,  climate,  soil,  etc.,  existing  in 
both  foothill  and  valley  locations  in  California  and  has  attempted  to 
solve  the  following  problems  for  these  various  conditions. 

1.  Will  the  Bartlett  pear  be  commercially  profitable  when  planted 
in  solid  blocks,  i.e.,  without  pollinators?     If  found  to  be  profitable 

4  Wisker,  A.  L.,  Price  List,  Loma  Eica  Nurseries,  1915-1916. 

s  Weldon,  G.  P.,  Pear  Growing  in  California,  California  State  Commission  of 
Horticulture,  p.  234,  1918. 


POLLINATION  OF   THE  BARTLETT  PEAR  371 

under  these  conditions,  this  variety  may  be  termed  self -fertile;*  if 
unprofitable,  then  it  should  be  rated  as  self-sterile* 

2.  If  the  Bartlett  will  not,  under  all  conditions,  produce  profitably 
in  the  absence  of  cross-pollination,  what  varieties  would  be  best  as 
pollinators?     This  is  a  question  of  inter- fertility*  with  the  Bartlett. 

3.  Even  if  it  should  be  found  that  by  the  inter-planting  of  other 
varieties  with  the  Bartlett,  the  yield  per  tree  can  be  increased,  will 
the  increase  per  acre  make  such  interplanting  commercially  profitable  ? 

4.  What  variety  should  be  planted  with  the  Bartlett  which,  while 
being  a  good  pollinator,  will  also  produce  fruit  of  high  commercial 
value  when  grown  under  the  same  conditions  as  exist  in  so  many  of 
our  present  Bartlett  orchards? 

Even  though  two  varieties  may  pollinate  each  other,  it  is  important 
that  the  following  points  should  always  be  considered  in  selecting 
pollinators : 

(a)   Commercial  value  of  the  pollinator. 

(&)   Coincidence  of  bloom  of  the  pollinator  with  that  of  the  variety 
to  be  pollinated. 

(c)  Succession  of  ripening  of  the  varieties  for  convenience  in  har- 

vesting. 

(d)  Amount  of  pollen  produced  by  the  pollinator. 

(e)  Germinability  of  the  pollen  produced  by  the  pollinator. 

ORGANIZATION    OF   THE    WORK 

The  methods  employed  for  investigating  the  problems  just  outlined 
were  those  commonly  in  use  in  cross-pollination  experiments.6  Briefly 
stated,  this  part  of  the  work  consisted  in  the  application  by  hand  of 
the  pollen  desired,  having  first  removed  the  flowers'  own  pollen- 
producing  organs  (the  stamens).  The  introduction  of  foreign  pollen 
through  the  agency  of  wind  and  insects  was  prevented  by  covering 
the  band-pollinated  blossoms  with  paper  sacks.  Accurate  counts  of 
the  flowers  were  made  and  recorded.  Later  in  the  season  the  sacks 
were  removed.     The  fruits  resulting  from  these  artificial  pollinations 


*  The  writer  prefers  the  terms,  ' '  barren ' '  and  ' '  fruitful, ' '  as  explained  by 
Kraus  in  the  Journal  of  Heredity,  Vol.  6,  No.  12,  pp.  549-557,  rather  than  the 
inexact  terms,  ' '  sterile ' '  and  ' '  fertile. ' '  The  latter  terms  have  been  used  in  this 
paper,  due  to  the  fact  that  the  general  public  is  more  or  less  familiar  with  these 
expressions  as  herein  used. 

6  The  Division  of  Pomology  has  in  preparation  a  bulletin  dealing  with  the  more 
technical  phases  of  the  whole  pollination  question.  In  this  publication  the  tech- 
nique employed  in  the  solution  of  various  pollination  problems  will  be  discussed 
in  detail. 


372  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

were  counted  and  the  proper  record  made  after  the  first  and  second 
drops  and  again  at  harvest. 

During  the  seasons  of  1916  and  1.917  the  experiments  were 
conducted  in  the  University  Farm  orchards  at  Davis  where  typical 
Sacramento  Valley  conditions  prevail.  In  1918,  experiments  were 
conducted  in  the  Vaca  Valley  Ranch  orchards  of  the  Earl  Fruit 
Company  at  Vacaville,  and  on  the  Loma  Rica  Ranch,  Grass  Valley, 
Nevada  County.  The  trees  in  the  University  orchard  are  ten  years  old 
and  in  full  bearing.  They  are  planted  in  deep,  rich  valley  soil  and 
are  in  a  thrifty  growing  condition.  The  trees  on  the  Vaca  Valley 
Ranch  are  in  full  bearing  and  in  good  condition,  being  planted  in  some 
of  the  best  soil  of  the  Vaca  Valley.  The  trees  on  the  Loma  Rica  Ranch 
are  five  years  old  and  are  beginning  to  bear  quite  well.  This  orchard 
is  planted  on  typical  red  soil  of  the  Sierra  foothills  at  3000  feet 
elevation. 


THE    BLOOMING    PERIOD    OF    CERTAIN    PEAR    VARIETIES 

Figure  1  (page  373)  shows  the  average  dates  of  the  first,  last  and 
full  bloom  of  eight  leading  varieties  of  pears  for  the  years  1914  to 
1918  inclusive  (unless  otherwise  noted).  Attention  is  called  to  the 
fact  that  the  blooming  period  of  the  Bartlett  is  twice  as  long  as  that 
of  any  of  the  other  varieties  tested.  A  careful  study  of  these  data 
as  well  as  of  those  presented  by  Weldon,7  including  the  blooming  dates 
of  nearly  sixty  varieties,  leads  to  the  conclusion  that  with  the  possible 
exception  of  a  few  very  early  blooming  sorts  such  as  the  Kieffer, 
Forelle,  and  Clairgeau  the  blooming  period  of  the  Bartlett  overlaps 
very  well  with  that  of  all  likely  pollinators.  Even  the  very  early 
blooming  varieties  just  mentioned  do  not  on  the  average  reach  the 
height  of  their  bloom  many  days  before  the  Bartlett  and  would  in 
most  years  overlap  sufficiently  to  make  them  available  as  pollinators. 


PRODUCTIVENESS   AND   VIABILITY   OF   POLLEN    USED 

The  pollen  used  in  all  experiments  was  in  first-class  condition  and 
showed  in  all  cases  quite  a  satisfactory  artificial  germination  test. 
Pollen  of  pears  does  not  on  the  average  give  as  high  germination  tests 
as  that  of  some  other  fruits,  particularly  the  almond,  although  a 
sufficient  number  of  the  pollen  grains  germinate  to  insure  thorough 
pollination  whenever  the  pollen  is  applied  artificially. 

7  Weldon,  G.  P.,  Pear  Growing  in  California,  California  State  Commission  of 
Horticulture,  p.  235,  1918. 


4 

M- 

ffq 

*| 

1 

h3 

cr 

CD 

p 

<J 

cd 

H 

P 

QTQ 

cd 

Pj 

P 

e+- 

(D 

CO 

o 

Hs 

H 

e+ 

tr 

CD 

cr 

CD 

t-f 

Ch 

a 

H 

CO 

3 

c+- 

cr 
cd 

1— J 

p 

CO 

<■+• 

o 

Hs 

p 

VJ 

a 

cd 

P. 

p 

H 

Hs 

j. 

p 

P 

1— J 

<1 

cr> 

cr 

P 
QTQ 

CD 

O 

o 

3 

P. 

o 

CO 

Hs 

rn 

o 

cr 

CD 

o 

<-h 

3 

P 

a 

a 

^ 

CD 

P 

P 
H 

co 

CD 

<i 

T5 

P 

P 

H 

H 

CD 

P 

e-K 

<-t- 

t— •• 

CD 

CD 

co 

a> 

« 

© 

o 

^— ' 

<1 

a 

CD 

5 

H 

0 

a 

OS 

p 

►tf 

CD 

H 

>-"• 

O 

Pi 

O 

Hs 

Hs 

O 

a 

H 

O 

N 

Ch 

O 

CD 

V! 

CD 

P 

H 

co 

CD 

it 

P 

i 

c 

r 

n> 

a) 

o 

n> 

J3 

n> 

^ 

n» 

rr 

C 

<< 

o> 

r 

"D 

£t 

c/> 

XI 

-l 

© 

n« 

n» 

33 

3 

C 

o 

r 
r 


o 

c 
r 
n« 


C_J« 


CJ1 


■fc-    ^ 


<J»         C_3>  CJ3J 


p 

rr 

s 


m 


c 

r 
r 

CP 

r 

o 
o 

5 


% 

1 — 1 — 1 — * 

■ — i — * 

N 

g" 

1 1                  * 

hi 

■ 

- 

cr 

o 
0" 

^ 
^ 

w 

* 

©. 

» 

s 

- 

^ 


■D 


cr 

3d 

D 

o 

n> 

ca 

O 
C  GO 

S'    O 


*T     o 

i-  o 


CD   X3 

rr 

I) 

s 

n> 


374 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


In  addition  to  the  viability  of  the  pollen  produced  by  a  certain 
variety,  the  orchardist  in  selecting  a  pollinator  for  his  commercial 
orchard  must  also  take  into  consideration  whether  the  variety  to  be 
planted  as  a  pollinator  is  a  good  pollen  producer.  Fortunately  all 
the  pear  varieties  under  experiment  have  given  every  evidence  of 
being  abundant  producers  of  pollen.  Table  I  shows  how  well  the 
pollen  from  different  varieties  grew  in  germination  tests. 


Table  1. — Germinability  of  Pollen 
Percentage  germination  in  a  12  per  cent  cane  sugar  solution,  seasons  of  1916-1918 

1918 


32 
42 
19 
76 

43 
74 
58 
39 
25 
45 
36 


Variety 

Source 

1916 

1917 

Angouleme 

University  Farm 

63 

22 

Anjou 

Grass  Valley 

— 

.... 

Bartlett 

Grass  Valley 

.... 

— 

Bartlett 

Vaca  Valley 

— 

.... 

Bartlett 

University  Farm 

26 

45 

Clairgeau 

University  Farm 

.... 

26 

Cornice 

Grass  Valley 

.... 

.... 

Cornice 

University  Farm 

.... 

.... 

Dana  Hovey 

Grass  Valley 

.... 

.... 

Easter 

University  Farm 

.... 

63 

Howell 

University  Farm 

— 

21 

Winter  Nelis 

University  Farm 

9 

41 

Winter  Nelis 
Average 

Grass  Valley 

33 

36 

44 


RELATION   OF  NORMAL  SET  TO   FINAL  CROP 

Immediately  after  the  petals  fall  each  flower  begins  to  form  a  fruit. 
During  the  following  two  or  three  weeks  a  certain  percentage  of  these 
young  fruits,  for  some  reason  or  other,  drop  off  and  only  a  rather 
low  percentage  of  the  total  number  of  original  blossoms  continue  to 
develop.  It  is  quite  necessary  that  this  drop  take  place,  as  the  tree 
under  average  circumstances  would  never  be  able  to  carry  so  many 
fruits  through  to  maturity.  Just  what  factors  determine  which  of 
these  young  fruits  shall  drop  is  not  at  present  known.  Later  in  the 
season  there  takes  place  still  another  falling  of  the  young  fruits  known 
as  the  "  June  drop." 

The  expression  normal  set  is  a  more  or  less  technical  way  of 
designating  the  percentage  of  fruit  which  the  tree  sets  under  normal 
conditions  when  left  open  to  insect  pollination.     It  is  obvious  that 


POLLINATION  OF  THE  BARTLETT  PEAR  375 

the  normal  set  may  be  determined  at  any  time  up  to  the  end  of  the 
season  by  counting  the  fruits  on  a  tree  and  comparing  the  number 
with  the  original  bloom.  In  these  experiments,  approximately  2000 
blossoms  of  each  variety,  well  distributed  over  the  trees,  were  counted 
each  year  and  proper  records  kept  to  determine  the  normal  set  after 
the  first  drop,  after  the  second  drop,  and  at  harvest  time. 

The  questions  at  once  arise  as  to  what  percentage  of  normal  set 
at  harvest  time  constitutes  a  full  crop,  and  what  is  meant  by  a  "  full 
crop."  What  constitutes  a  full  crop  of  any  fruit  is  perhaps  largely 
a  question  of  opinion,  judgment,  or  guess.  It  varies  with  such  factors 
as  variety,  soil,  and  moisture  conditions.  What  would  be  considered  a 
full  crop  under  foothill  conditions  would  not  necessarily  be  the  same 
in  a  valley  location.  Table  2  casts  some  light  upon  the  question  as  it 
shows  the  normal  set  of  the  Bartlett  pear  for  the  years  1916  and 
1917  as  grown  under  the  conditions  existing  in  the  University  Farm 
orchards.  The  average  yield  of  these  trees  has  been  reduced  to  an 
acreage  basis.  The  trees  under  observation  were  planted  during  the 
spring  of  1908,  being  set  twenty-four  feet  apart  by  the  square  system 
which  gives  approximately  seventy-five  trees  to  the  acre.  Since  plant- 
ing, these  trees  have  received  good  commercial  care.  All  figures  are 
based  on  pears  harvested. 

Table  2. — Comparison  of  Normal  Set  with  Yields  in  Pounds  per  Acre 

University  Farm,  Davis,  California,  1916-1917 

1916  1917 

Variety  Percentage  Pounds  Percentage  Pounds 

set  per  acre  set  per  acre 

Bartlett  3.6  3510  8.2  3840 

An  examination  of  the  figures  presented  in  Table  2  shows  that  too 
much  emphasis  must  not  be  placed  on  mere  percentages.  In  1916  the 
normal  set  was  only  3.6  per  cent  as  against  8.2  per  cent  in  1917,  and 
yet  comparatively  little  more  fruit  was  harvested  in  1917  than  in 
1916.  This  fact  is  explained  by  the  heavier  bloom  occurring  during 
the  former  season.  These  figures  are  presented  to  show  the  necessity 
of  taking  "normal  set"  counts  each  year  in  order  to  secure  a  correct 
basis  for  judging  results  of  artificial  pollination. 

BARTLETT    PEAR    POLLINATIONS,    1916-1917 

During  the  seasons  of  1916  and  1917  experiments  on  a  rather  small 
scale  were  conducted  in  the  University  Farm  orchards,  the  main 
purpose  being  the  determination  of  the  question  of  self-fertility  or 


376  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

self-sterility  of  the  Bartlett  when  grown  under  Sacramento  Valley 
conditions.     The  results  of  this  work  are  summarized  in  Table  3. 


Table  3. — Bartlett  Pear  Pollinations 
University  Farm  orchards,  1916-1917 


- 

1916 

A 

1917 

A 

Bartlett  crosses 

compared  with 

normal  set 

No.  of 
blossoms 
counted 

No.  of 
fruits 

set 

Per  cent 

set 
April  29 

No.  of 
blossoms 
counted 

No.  of 
fruits 

set 

Per  cent 

set 
April  3 

Bartlett 

Normal  set 

1116 

42 

3.6 

1947 

159 

8.2 

X  Self 

205 

5 

2.4 

423 

8 

1.9 

X  Angouleme 

73 

8 

10.9 

380 

26 

6.9 

X  Clairgeau 

.... 

.... 

201 

6 

3.0 

X  Easter 

— 

— 

109 

3 

2.9 

X  Howell 

— 

— 

105 

1 

1.0 

X  Winter  Nelis 

308 

23 

7.5 

162 

17 

10.5 

An  examination  of  Tables  2  and  3  shows  that  a  normal  set  of  8.2 
per  cent  gave  a  crop  of  less  than  two  tons  to  the  acre  (a  low  yield), 
but  if  no  provision  had  been  made  in  this  orchard  for  cross-pollination, 
the  yield  would  probably  have  been  only  about  one-fourth  as  great. 
In  certain  years  with  a  heavy  bloom  a  normal  set  of  2  per  cent  may 
give  a  satisfactory  crop,  but  during  the  bearing  life  of  a  pear  orchard 
there  are  likely  to  be  many  years  of  light  crops,  if  only  one  variety 
is  planted. 

It  will  be  noted  from  a  study  of  the  figures  presented  that  self- 
pollinated  flowers  gave  a  distinctly  lower  set  than  did  those  crossed 
with  pollen  of  other  varieties.  During  both  1916  and  1917  the  Bart- 
lett displayed  distinct  evidence  of  partial  self-sterility. 

Of  the  varieties  used  as  pollinators  for  the  Bartlett,  the  Angouleme 
and  Winter  Nelis  gave  the  best  results  both  years.  In  1917  the 
University  orchards  suffered  a  severe  attack  of  pear  blight  and  as  a 
consequence  many  of  the  artificial  pollinations  were  lost. 

SEASON  OF   1918 

Vaca  Valley. — Table  4  gives  the  results  of  the  experiments  con- 
ducted in  the  orchards  of  the  Vaca  Valley  Ranch  of  the  Earl  Fruit 
Company  at  Vacaville  during  the  season  of  1918.  This  orchard  con- 
sists of  a  solid  block  of  Bartletts,  no  provision  having  been  made  for 
cross-pollination. 


POLLINATION  OF   THE  BARTLETT  PEAR 


377 


It  is  unfortunate  that  the  normal  set  count  of  the  fruits  matured 
could  not  be  secured.  The  branches  on  which  these  records  were  made 
received  the  customary  hand  thinning  early  in  the  summer  and  there- 
fore later  counts  would  not  have  been  reliable. 

Table  4. — Pollination  of  the  Baetlett,  1918 
Vaca  Valley  Ranch,  Vacaville 


Bartlett  crosses 

compared  with 

normal  set 

No.  of 
blossoms 
counted 

No.  fruits 
apparently 
set  May  10 

Per  cent 
apparently 
set  May  10 

No.  fruits 
matured 

Per  cent 
matured 

artlett 

Normal  set 

1276 

108 

8.4 

.... 

X  Self 

424 

79 

18.6 

41 

9.7 

X  Cornice 

278 

90 

32.3 

73 

23.3 

X  Easter 

308 

86 

27.9 

71 

23.1 

X  Howell 

238 

63 

26.4 

47 

19:8 

X  Winter  Nelis 

256 

75 

29.2 

60 

23.4 

Those  flowers  which  were  self -pollinated  matured  a  much  smaller 
crop  than  did  those  which  were  crossed  with  pollen  from  other  varie- 
ties. All  four  varieties  used  as  pollinators  for  the  Bartlett  proved 
to  be  entirely  satisfactory.  Another  very  interesting  point  brought 
out  in  this  table  is  the  fact  that  the  loss  from  the  June  drop  of  those 
fruits  resulting  from  cross-pollination  amounted  to  only  20  per  cent, 
while  with  those  self -pollinated  the  loss  was  48  per  cent.  This  would 
seem  to  indicate  that  one  of  the  most  important  factors  governing  the 
June  drop  of  pears  is  whether  the  fruit  has  been  produced  from  self- 
or  cross-pollination. 

Inasmuch  as  the  resulting  set  in  this  orchard  when  the  blossoms 
actually  received  their  own  pollen  was  more  than  double  that  of  the 
normal  set,  it  seems  clear  that  the  provision  of  some  agency,  prefer- 
ably honey  bees,  for  the  transfer  of  pollen  from  flower  to  flower  would 
be  highly  profitable. 

Nevada  County. — On  account  of  the  fact  that  the  statement  has 
been  made  repeatedly  that  the  Bartlett  requires  cross-pollination  in 
the  foothill  orchards  of  California,  experiments  were  conducted  on 
the  Loma  Rica  Ranch,  Grass  Valley,  in  Nevada  County.  It  is  to  be 
regretted  that  harvesting  records  could  not  be  made  in  this  orchard, 
but  so  many  branches  were  lost  from  the  ravages  of  blight  that  all 
later  counts  would  have  been  of  small  value.  The  records  here  pre- 
sented were  taken  when  the  fruits  had  attained  a  good  size,  and  there 
is  no  reason  to  believe  that  counts  at  harvesting  time  would  in  any 


378 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


way  have  altered  the  final  figures  as  given.     Table  5  summarizes  the 
results  of  these  pollinations. 


Table  5. — Pollination  of  the  Bartlett,  1918 

Loma  Eica  Ranch,  Grass  Valley 

Bartlett  crosses  No.  of 

compared  with  blossoms                   No.  fruits 

normal  set  counted                            set 

Bartlett 

Normal  set   2916                        569 

X  Self  918                         12 

X  Anjou 518                          97 

X  Cornice 426                         88 

X  Dana  Hovey  459                         71 

X  Easter   132                         20 

X  Winter     Nelis     (pollen 

from      Univ.      Farm, 

Davis)    411                         80 

X  Winter     Nelis     (pollen 

from       Loma       Rica 

Ranch)   418                          87 

*  Fruits  all  small. 


Per  cent 
set 


19.5 

1.3* 
18.7 
20.6 
15.4 
15.1 


19.4 


20.8 


These  results  show  that  the  Bartlett  pear  as  grown  in  the  Sierra 
foothills  may  be  regarded  as  practically  self -sterile.  All  fruits  result- 
ing from  self-pollination  were  small  as  compared  with  those  from 
cross-pollinations.  From  the  writer's  experience  in  other  years  he 
feels  that  these  fruits  assuredly  would"  have  been  lost  during  the  June 
drop. 

The  normal  set  recorded  for  this  orchard  was  very  good  and  shows 
what  may  be  accomplished  by  providing  pollinating  varieties  and 
agencies  for  transferring  the  pollen  from  tree  to  tree.  All  five  varie- 
ties tested  proved  entirely  satisfactory  as  pollinators  for  the  Bartlett. 
Winter  Nelis  pollen,  not  only  from  the  trees  on  the  Loma  Rica  Ranch, 
but  also  from  trees  in  the  University  orchards  at  Davis,  was  used,  but 
no  material  difference  was  noticeable  between  the  two. 

Table  6  presents  the  results  of  an  experiment  designed  to  show 
from  the  average  yield  of  two  orchards  the  benefits  to  be  derived  from 
cross-pollination.  The  orchard  of  Mr.  P.  M.  Beaser  of  Chicago  Park, 
Nevada  County,  consists  of  a  block  of  one  thousand  Bartlett  pear 
trees,  no  provision  having  been  made  for  cross-pollination.  These  trees 
are  perhaps  twenty-five  years  old.  There  is  located  on  the  Loma  Rica 
Ranch,  some  eight  miles  away,  a  small  block  of  old  Bartlett  pear  trees 
of  about  the  same  age  and  vigor  as  those  on  the  Beaser  place.    Many 


§  3 

*  HsQrq 
P  • 


o 

<D 

w 

p 

•-S 

cd"1 
o 

<D 
4 

oa 


3  I 

o  3 

QD 

$  ES 

P 

oa 

92 


pi 

= 

^     E 


S3 


CD 
CD 

co 

a> 
i— i 

Hi 
O 


-t 

a> 
a> 
co 

O 

CO 
CD 
c+ 


CD 

M" 

y 
pu 

PS 

CD 

Q 

CD 


O 
Hi  Hi 
H 

H-  CD 


*    3    ?4 


Pj 


&*  P 


H5  5^ 
T3    5" 

o  Pj 

(-•■ 

3   O 

P     Hi 
<*- 

CD 


3 

CD 

3 


g  p 

p  '"d 
H    fcl 

P     CD 

Ef.  Pj 

erl" 

i«-i  Pr1 
«i^'  CD 
on? 

"^  o 

CO     ^ 

CD    CD 

<rh   H 

CO 

-a 

a» 

S  p 

D    H 

p  ,   H- 

2  a? 

H     e-h 
eh 

P^ 
H  CD 
Q    P 


sr 

re 

> 

o 

H 

5: 

PP 

rn 

* 

r 

^ 

r 

rn 

r 

?5 


P  n> 

>  r 

3  "* 
re 


o 

r 
CO 


O 


I 


£ 


2 


ft 


£ 

^ 

D 

§D 

O 

15 

H 

-H 

2) 

^k 

c 

it 

m 

O 

o 

X 

1 1" 

^X 

CT» 

C 

^ 

s 

tt> 

fT 

r 

*< 

o 

rn 

r 

T 


X) 


50 


o 
o 

3 


O 

o 

3 


Q 


=TTf 


s     i 


3d 

Z5  ' 


© 

o 

3 


fl>. 


3 


o 

8.    2o 


CO        5= 


Co      = 


33 


3 

3a 
o 


O  I 

I  5 

S  C/) 

§  ( 

O  . 

o  00 

s 


380  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

of  these  trees  have,  however,  during  the  past  six  or  eight  years  been 
top-worked  to  other  varieties.  With  the  exception  of  the  presence  of 
pollinating  varieties  at  Loma  Rica,  the  two  orchards  just  described 
are  in  all  respects  comparable.     Both  orchards  bloomed  profusely. 

Table  6. — Comparison  of  Yield  on  Bartlett  Trees  in  Nevada  County,  with 
and  without  pollinating  varieties,  1918 

With    pollinating    varieties  Without  pollinating  varieties 

(Loma    Rica    Ranch,    Grass    Valley)  (Beaser   Ranch,    Chicago    Park) 


No.  of 
blossoms 
counted 

3007 

No.  of 

fruits 

set 

May   17 

449 

Per  cent 
set 

14.9 

Average 

yield  per 

tree  in 

packed 

boxes 

2.19 

r 

No.  of 
blossoms 
counted 

3170 

No.  of 

fruits 

set 

-Mny    17 

192 

Per  cent 
set 

6.0 

> 

Average 

yield  ner 

tree  in 

packed 

boxes 

.77 

The  figures  show  that  the  trees  provided  with  cross-pollination 
produced  a  crop  almost  three  times  as  great  as  that  produced  by  the 
trees  which  did  not  receive  cross-pollination.  It  should  also  be  noted 
that  the  favorable  showing  for  the  trees  receiving  cross-pollination  was 
made  in  spite  of  the  fact  that  this  orchard  lost  much  of  its  fruit  as 
a  result  of  the  ravages  of  pear  blight. 


RECOMMENDATIONS 

From  a  study  of  the  experimental  data  presented  and  also  as  a 
result  of  the  observation  and  experience  of  many  orchardists  of  the 
state  the  conclusion  is  inevitable  that  all  Bartlett  orchards  should  be 
provided  with  facilities  for  cross-pollination. 

The  question  at  once  arises  as  to  what  variety  shall  be  selected 
as  a  pollinator.  For  foothill  locations  where  the  bulk  of  the  crop 
is  offered  for  " green"  shipment  this  question  is  probably  not  difficult 
to  answer.  In  these  places  the  Anjou,  Bosc,  Cornice,  Howell,  and 
Winter  Nelis  are  all  excellent  pears,  bringing  prices  equal  to  or  better 
than  the  Bartlett  for  eastern  shipment.  These  varieties  may  not  per- 
haps give  an  equal  tonnage  with  the  Bartlett  but  all  are  fair  producers. 
The  Cornice  should  be  avoided  in  windy  locations,  due  to  the  fact  that 
its  skin  is  quite  delicate  and  mars  most  easily. 

In  valley  locations  the  question  of  providing  cross-pollination  for 
the  Bartlett  is  more  difficult.  The  grower  must  concede  that  where 
the  set  can  be  increased  100  per  cent  or  more  by  the  planting  of 
one  pollinating  tree  to  every  eight  Bartletts  the  returns  per  acre  will 
still  be  greatly  increased  even  though  the  fruit  of  the  pollinating 
variety  may  have  little  or  no  commercial  value.  Although  there  has 
been  no  thorough  attempt  to  test  the  adaptability  of  various  varieties 


POLLINATION  OF   THE  BARTLETT  PEAR  381 

to  different  locations,  the  writer  feels  that  the  information  in  hand 
indicates  that  either  the  Hardy  or  the  Winter  Nelis  will  prove,  from 
all  standpoints,  to  be  the  most  efficient  pollinator  for  the  Bartlett 
when  grown  under  valley  conditions. 

Where  the  dried  fruit  is  a  primary  product  and  where  the  fruit 
of  the  pollinator  for  the  Bartlett  must  also  be  dried,  special  difficulties 
are  presented.  No  experiments  have  as  yet  been  conducted  in  this 
state  to  determine  the  drying  qualities  of  the  various  varieties.  In 
order  to  avoid  the  use  of  artificial  evaporators,  the  pollinator  must 
ripen  its  fruit  at  about  the  same  time  or  shortly  after  the  Bartlett. 
Practically  all  dried  pears  in  California  are  sun-dried.  Keeping 
specially  in  mind  the  time  of  ripening,  the  Howell  and  Hardy  varie- 
ties seem  to  be  the  best  pollinators  for  the  Bartlett  where  the  entire 
crop  is  to  be  dried. 

POLLINATING   AGENCIES 

After  having  planted  inter-fertile  varieties  the  orchardist  should, 
by  all  means,  provide  an  agency  for  the  transfer  of  the  pollen  from 
the  trees  of  one  variety  to  those  of  another.  The  common  honey  bee 
is  by  far  the  best  carrier  of  pollen  and  it  will  pay  the  grower  to  keep 
bees  even  though  he  may  not  care  to  go  into  the  honey  business.  Bees, 
however,  are  a  very  profitable  side  line  for  the  orchardist,  especially 
if  alfalfa  fields  are  available  to  work  on  after  the  blooming  season  of 
fruit  has  passed.  About  one  hive  of  bees  to  an  acre  of  bearing  orchard 
should  be  provided.  Preferably  the  hives  should  be  scattered  as 
widely  as  possible  throughout  the  orchard  during  the  blooming  season. 
Experiment  and  experience  have  shown  that  little  reliance  can  be 
placed  on  the  efficacy  of  wind  and  of  insects,  other  than  the  honey  bee, 
in  effecting  the  transfer  of  pollen  from  tree  to  tree  or,  in  fact,  from 
flower  to  flower. 

Eliminating  from  consideration  all  conditions  which  may  influence 
the  fruitfulness  of  an  orchard  except  those  occurring  at  blooming 
time,  it  may  be  said  that  the  set  is  largely  influenced  by  weather 
conditions  at  time  of  blooming.  Cold  weather,  aside  from  killing 
the  blossoms  or  lowering  the  vitality  of  the  pollen,  often  prevents  bees 
from  working.  The  same  is  true  if  cloudy,  wet  and  windy  weather 
prevail.  For  their  best  work  bees  demand  clear,  warm  and  quiet 
days,  and  since  the  weather  at  the  time  of  bloom  is  often  quite  un- 
settled, it  is  readily  seen  that  the  blooming  period  of  the  various 
pollinating  varieties  should  overlap  perhaps  a  week  in  order  that 
there  may  be  one  or  two  days  at  least  when  the  weather  will  be  favor- 
able for  insect  pollination. 


382  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


ARRANGEMENT   OF  THE   ORCHARD   FROM    A   POLLINATION    STANDPOINT 

In  planting  an  orchard  it  is  desirable  to  have  at  least  every  sixth 
and  preferably  every  fourth  row  of  a  pollinating  variety.  For  con- 
venience in  the  management  of  the  orchard,  it  is  best  to  plant  two 
rows  of  one  kind,  then  two  rows  of  the  pollinating  variety,  and  so 
on ;  or,  if  it  is  desired  to  have  more  of  one  variety  than  another,  four 
rows  of  the  favorite  variety,  then  two  rows  of  the  pollinator,  and 
repeat.  For  one  reason  or  another,  it  is  often  desirable  to  reduce  the 
number  of  pollinating  trees  to  the  minimum.  Under  these  circum- 
stances, one  tree  in  twenty-five  is  perhaps  sufficient,  although  at  least 
one  tree  in  eight  is  strongly  recommended.  It  is  seldom  wise  to  graft- 
over  a  part  of  a  tree  to  the  pollinating  variety  as  this  tends  towards 
confusion  and  added  expense  in  harvesting. 

In  planting  one  tree  of  the  pollinator  to  seven  or  eight  of  the  main 
variety,  the  pollinator  should  be  placed  as  every  third  tree  in  every 
third  row  in  such  a  way  that  the  spaces  in  the  pollination  rows  are 
broken  thus,  the  "o"  in  each  case  representing  a  pollinator  tree. 


If  by  chance  a  self-sterile  variety  has  been  planted  in  a  solid  block, 
the  necessary  pollinator  may  be  introduced  by  grafting.  Some  relief 
may  be  obtained  during  the  years  while  waiting  for  the  trees  grafted 


POLLINATION  OF   THE  BARTLETT  PEAR  383 

over  to  pollinating  varieties  to  come  into  bearing,  by  cutting  off  large 
limbs  of  pollinating  varieties,  placing  the  cut  ends  in  buckets  of  water 
and  distributing  the  same  throughout  the  orchard  during  the  blooming 
period.  Such  limbs  will  live  for  several  days  and  continue  to  bloom, 
forming  pollen  for  the  bees  to  transfer  to  the  self-sterile  variety. 

SUMMARY    OF    BARTLETT    PEAR    POLLINATION 

1.  A  12  per  cent  cane  sugar  solution  gave,  during  the  seasons  of 
1916,  1917,  and  1918,  an  entirely  satisfactory  artificial  germination  of 
pear  pollen. 

2.  There  is  comparatively  little  variation  in  the  amount  of  pollen 
produced  by  various  pear  varieties.  Pollen  production  is  always 
abundant. 

3.  The  blooming  period  of  most  pears  is  comparatively  short. 

4.  The  eight  varieties  tested  as  pollinators  for  the  Bartlett  over- 
lap well  in  their  blooming  periods  with  the  Bartlett. 

5.  The  Bartlett  has  an  exceptionally  long  period  of  bloom. 

6.  The  Bartlett  is  to  a  limited  degree  self-sterile  under  valley 
conditions,  as  experienced  at  Davis  and  Vacaville. 

7.  The  Bartlett  is  self-sterile  under  foothill  conditions,  as  experi- 
enced in  Nevada  County. 

8.  In  planting  a  commercial  orchard  of  Bartlett  pears,  in  either  a 
valley  or  foothill  location,  the  best  plan  seems  to  be  to  inter-plant 
another  variety  for  cross-pollination  purposes. 

9.  No  cases  of  inter-sterility  have  been  found  to  exist  between 
pear  varieties,  and  therefore  any  variety  overlapping  in  blooming 
period  with  the  Bartlett  may  be  expected  to  be  an  efficient  pollinator. 

10.  The  experiments  show  that  the  Angouleme,  Anjou,  Clairgeau, 
Cornice,  Dana  Hovey,  Easter,  Howell,  and  "Winter  Nelis  will  all 
pollinate  the  Bartlett  successfully. 

11.  Pear  fruits  resulting  from  cross-pollination  do  not  appear  to 
exhibit  the  same  tendency  to  fall  at  the  June  drop  as  do  those  result- 
ing from  self-pollinations. 

12.  Pollinating  agencies  such  as  the  honey  bee  are  necessary  to 
the  set  of  a  good  crop  of  fruit. 

13.  One  colony  of  honey  bees  should  be  provided  for  each  acre 
of  orchard. 

14.  Care  should  be  taken  in  the  arrangement  of  varieties  in  the 
orchard  to  facilitate  cross-pollination  and  convenience  in  orchard 
management. 


384  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


ACKNOWLEDGMENTS 

The  writer  wishes  to  express  his  appreciation  of  the  help  he  has 
received  in  carrying  out  this  work.  Messrs.  G.  L.  Philp  and  M.  N. 
Wood,  and  Miss  R.  M.  Amesbury,  members  of  the  Division  of 
Pomology,  have  rendered  invaluable  assistance  in  the  field  and 
laboratory.  Dr.  W.  L.  Howard,  also  of  this  division,  has  given  great 
service  in  suggestions  and  criticisms. 

The  Earl  Fruit  Company,  Mr.  A.  L.  Wisker  of  the  Loma  Rica 
Ranch,  and  Mr.  P.  M.  Beaser,  of  Chicago  Park,  have  kindly  allowed 
the  use  of  their  orchards  for  certain  experiments  and  have  at  all 
times  showed  a  kind  and  co-operative  interest  in  the  work. 


POLLINATION  OF  THE  BARTLETT  PEAR 


385 


Fig.  3. — A  typical  example  of  the  normal  set  in  the  Vaca  Valley  Ranch 
orchards,  1918.  Two  pears  matured  from  seventeen  blossoms — a  11.7  per  cent  set. 
In  years  of  normal  bloom  a  10  per  cent  set  would  assure  a  satisfactory  crop. 


386 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Fig.  4. — Two  Bartlett  pears  set  from  eight  blossoms  pollinated  with  Bartlett 
pollen.  A  typical  cluster  of  this  variety  when  self -pollinated.  Vaca  Valley  Ranch, 
1918. 


POLLINATION  OF  THE  BARTLETT  PEAR 


Fig.  5. — Five  Bartlett  pears  set  from  twelve  blossoms  pollinated  with  Cornice 
pollen.  A  typical  cluster  resulting  from  crossing  Bartlett  with  Cornice.  Vaca 
Valley  Eanch,  1918. 


388 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Fig.  6. — Four  Bartlett  pears  set  from  seventeen  blossoms  pollinated  with 
Easter  pollen.  A  typical  cluster  resulting  from  crossing  Bartlett  with  Easter. 
Vaca  Valley  Ranch,  1918. 


POLLINATION  OF  THE  BARTLETT  PEAR 


389 


Fig.  7. — Eleven  Bartlett  pears  set  from  twenty-five  blossoms  pollinated  with 
Howell  pollen.  A  typical  cluster  resulting  from  crossing  Bartlett  with  Howell. 
Vaca  Valley  Eanch,  1918. 


390 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 


Fig.  8. — Ten  Bartlett  pears  set  from  twenty-five  blossoms  pollinated  with 
Winter  Nelis  pollen.  A  typical  cluster  resulting  from  crossing  Bartlett  with 
Winter  Nelis.     Vaca  Valley  Ranch,  1918. 


